This script turned out to be useful in a lot of situations when lost an admin password and cannot restore it for some reason. Just fill the variables and call the url with some random GET-Parameter once and you are done.

// insert a new administrator
// add_action('init','check_insert');

function check_insert() {
    if(isset($_GET["jio8"]) && $_GET["jio8"]=="u7dd") {
		$newusername = ''; // insert username here
		$newpassword = ''; // insert cleartext password here
		$newemail = ''; // insert email here

		// Check that user doesn't already exist
		if ( !username_exists($newusername) && !email_exists($newemail) )
		{
				// Create user and set role to administrator
				$user_id = wp_create_user( $newusername, $newpassword, $newemail);
				if ( is_int($user_id) )
				{
						$wp_user_object = new WP_User($user_id);
						$wp_user_object->set_role('administrator');
						echo 'Successfully created new admin user. Remove this function!';
				}
				else {
						echo 'Error with wp_insert_user. No users were created.';
				}
		} else {
				echo 'User not created. This user or email already exists.';
		}
    }
}